It is the function of pipette tip racks to organize disposable pipette tips in a manner for convenient tip placement on a pipette. Such racks generally comprise a rigid base with vertical sides joined at contiguous edges and horizontally supporting a rigid pipette tip organizing tray having an array of pipette tip receiving holes extending there through. The pipette tips are organized and held vertically in the array of holes for ease of access by a pipette tip user. In this regard, the pipette tip user simply places a hand-holdable pipette over the rack and lowers a distal end of the pipette into a proximal or upper end of a vertically oriented pipette tip and presses down to affix the tip to the pipette. A similar operation is followed by the user when connecting a plurality of tips to a multiple tip pipette. U.S. Pat. No. 4,676,377 describes a conventional pipette tip rack of the type just described and U.S. Pat. No. 4,779,467 describes a multiple tip pipette.
Once all tips are dispensed from the tip rack, the rack may be discarded or reloaded with a new supply of pipette tips. The reloading of replacement pipette tips into the tip rack in a rapid, convenient manner is important to pipette users. In this regard, any packaging containing pipette tips for use in reloading pipette tips into a tip rack should arrange the pipette tips in a manner to accommodate direct dispensing of the tips into the array of holes in the organizing tray of the tip rack. Further, the packaging should guide and assist in centering the replacement pipette tips over the rack with the array of replacement tips aligned with the array of holes in the pipette tip rack organizing tray upon a lowering of the packaging onto the rack. Moreover, it is important that such packaging protect the replacement pipette tips from damage and contamination during shipping, handling and storage and provide for sterilization of the replacement tips by autoclaving or irradiation. Still further, when plastic materials are utilized for such packaging, it is particularly important to the preservation of our environment that (1) the plastic material be recyclable to the extent possible and (2) the packaging structure be thin, lightweight and of low mass to minimize the amount of non-biodegradable disposable material from such packaging. Furthermore, there is a need for refill packs for manually reloading reusable pipette tip racks with filter containing pipette tips such as the FilterPro of the Rainin Instrument Co., Inc., assignee of the present invention.
U. S. Pat. No. 5,392,914 assigned to the assignee of the present invention, describes pipette tip packaging systems and refill packs for pipette tip racks for loading new supplies of pipette tips into reusable tip racks and is incorporated herein by this reference. With one packaging system described in the patent, a technician grasps and positions a tubular cover containing a stack of support plates each containing an array of replacement pipette tips and centers the cover over an empty pipette tip rack. With distal ends of the tips in a lowermost one of the support plates extending into empty holes in the support tray of the pipette tip rack, the technician presses downward on a top or push plate in the tubular cover to push the stack of support plates downwardly within the cover effecting a release of the lowermost support plate and the array of tips supported thereby into the empty holes in the support tray of the tip rack. With another packaging system described in the patent, the technician places a refill pack over the top of the reusable tip rack and simply presses down on the top of the pack to release a support plate containing an array of replacement pipette tips into the empty tip rack. Then, when the technician desires to attach a pipette tip to a pipette, he follows the previously described method of placing a hand holdable pipette over the rack, lowering a distal end thereof into an upper end of a vertically oriented pipette tip and pressing down to affix the tip to the pipette.
The above described packaging systems and pipette tip rack refill packs have heretofore performed very well in the housing of replacement pipette tips and in the refill of empty pipette tip racks. However, with the recent advent of "micro"-size pipette tips having liquid intake volumes of about 10 microliters, it has been found that the pipette tip support plates included in the present versions of the packaging systems and refill packs do not provide adequate support for the proximal end portions of such "micro" tips against lateral rocking and displacement during shipping and use of the refill packs. This is primarily due to the narrow nature of the distal end portions of such tips and the relative low mass thereof compared to the upper or proximal ends of such tips. In essence, such micro pipette tips are "top heavy" and have a tendency to laterally rock on conventional support plates interfering with the efficient dispensing of the micro pipette tips as replacement tips into an empty pipette tip rack. Such a tendency to laterally rock in conventional refill pack support plates and in conventional tip rack support trays is also a characteristic of other top heavy pipette tips. Also, pipette tips having a taper angle in the region passing through the holes in conventional support plates and tip rack support trays sufficient to leave a clearance space between the tip and the support hole (large taper angle tips), have a tendency to rock laterally on the support plates and trays with resulting misalignment of the tips particularly when such tips are vertically displaced as during shipment and handling of refill packs and tip rack containing such tips.
U.S. Pat. No. 5,487,997 describes a pipette tip rack refill pack which includes a support plate having tapered holes for engaging and gripping vertically extending ribs on the proximal end portion of pipette tips as the ribs extend through the plate. Such friction gripping of the tips holds them securely within the pack and prevents lateral rocking of the tips while they are secured in the support plate. In use, however, the pack is intended to be placed over an empty tip rack with distal ends of the tips inserted into the holes in a support tray of the tip rack until the lower ends of the vertical ribs rest on a top of the support tray. In this position, the support plate is vertically spaced from the top of the support tray. To release the tips for dispensing from the tip rack, the support plate is forced downwardly to rest on top of the support tray. The tips are no longer laterally supported by the support plate and are free to rock laterally if they are micro or other top heavy pipette tips or large taper tips as previously defined.
Thus, there is a need for improved pipette tip packaging and refill packs which impart lateral stability to micro as well as other small volume pipette tips contained therein. The present invention satisfies such a need.